Fractionating column



2,983,494 7 .FRACTIONATING COLUMN' Erwin C. Handwerk, Lehigliton, Pa., assignor to American Metal Climax, Inc., New York, N.Y., a corpora tion of New York V I Filed Feb. 7, 1957, Ser. No. 638,849 1 8 Claims. (Cl, 261-110) This invention relates to the purification of metallic vapors and more particularly to apparatus adaptedflfor the fractional distillation of zinc to effect its seperation from contaminants such as iron, lead and cadmium.- 1

In 1935 fourteen U.S. Patents, Nos. 1,994,345 to l,-994,- 358, inclusive, were granted for zinc distillation and apparatus therefor. While the production ofrefined zinc based on fractional distillation has spread worldwidexand increased substantially in tonnage over the'years, the technology of.refining metallic zinc by fractional distillation years which sets forth an improvement ofsuchf columns.

The conventional practice has been to-form thezinc distillation column by stacking a, multiplicity of trays, each having side walls for the dual purpose of confining a pool of molten metal on the tray and of supporting the stacked trays in spaced relationship to one another. This type of structure is shown in the 1935 patents, .e.g., Figures 1 and 2 of US. Patent 1,994,349; when it is re membered that each tray is made of a refractory material, it will be readily appreciated that the trays in the lower portion of the column are particularly subject to cracking and like mechanical failures because of, the substantial superimposed load and because of thermal'shock due to dry boiling. Obviously, each failure is costly because of not only the longshut-down time required to cool and reheat the column but also the considerable labor necessary to rebuild practically the entire column to replace a damaged tray. in the lower portionthereof.

nited States PatentC ln lieu of these pan-shaped trays, U.S; Patent-l,99 4,349

alsoproposes the use of saucer plates (Figures .4 and 5) which are again stacked upon one another'and supported in spaced relationship by pins dependent from the lower side of each saucer'plate.- This proposal-has stilLan- 1 other handicap. Since the metallic vapors rising from the column condense to a large extentLonithewallspfthe column and it is not practicalto, seal the: edges of'each saucer plate to these walls, the condensed metalwill in a P e ed May. 9.1961

vention willbe apparent from the description which follows. In accordance with this in'v'ention, the trays of a fractionating column for metallic vapors are individually supported 'by the walls of the column, the inner sides of which have horizontal grooves or slots for the dual purpose ofholding edge portions of the trays and preventing the by-passing ofthe trays by the metal condensed on these walls. Being individually supported, the trays no longer have a load-bearing function and are free to expand and'contract with temperature changes'because they areloos'ely positioned in the supportingwall grooves. The depth of these grooves is made sufficient toiprovide a rea'sonably strong support for the trays and thejfull capacity of condensed metal accumulated thereon and to enstire the flow of metal condensed ontheinterionsur; faces of'the column preferentially'onto the trays.

In the accompanying drawing forming a part of this specification and showing a preferred embodiment of this invention without limiting the claimed invention thereto;

Figure 1 is a vertical section of a portion of a fractionating'colurnn formed of refractory materials wherein hot vaporsiare contactedwith liquid condensed from the vapors; and i5 5 *zrFig'ure 2 isa vertical section of the same fractionating columntaken through line 2-2 of Figure l. As shown in the drawings, the fractionating column comprises 'a tower 16 formed by'two pairs'of substantially parallelwalls ll, 12 and 13,;'1 4Farranged to providea tower opening having a rectangular horizontal cross-secti'on. "The-inner sides of-walls 11;, 12, '13, 14 are provided with vertically spaced horizontal grooves 15. A plurality of vertically spaced trayshave edge portions fitted loosely in' hor'izontalgrooves 15 which provide the sole support forthese trays. t n o Figure 1 shows that the tray at each level in the fractionating column consists of a pair of similar tray elements 16 or 17 of rectangular shape. Each pair of tray elements 16 disposed in the horizontal grooves 15 at one level in tower 10 abut one another along the vertical center line of tower 10, Whereas the pair of tray elements 17 in each of the grooves 15 at the next lower and next higher levels in tower 10 are laterally spaced from. one another and one edge portion of each tray element 17 which is parallel to the opening between the spacedelemerits 17 fits loosely in ahorizontal groove. 15. In short, pairs'of tray'elements 16 and 17 are alternately disposed at'adjacentlevels in tower'ltl so that hot vapors ascending throughtower 10 pass'through the space between each pair of tray elements 17 and flow around 'each pairof t'ray elements 16, While the hot vapors areflowing in this zigza'g'pattern, liquid condensed therefrom flows along each .tray element'17 toward theedge which'is not fitted into a horizontal groove-15, and spills overweir18 onto the? subjacent't'ray elemenr s. In turn, liquid flows from each jtray element 16 to its weir 19 where it. again overfi'ow'sdro'ppingto the subjacent tray element 17; It will drawing; tray elements '1'6 ai e supported in horizontal vision of a fractionating columnfor metallicvapors which is structurally simpler and moredurable, ;is 1easy t o. operate and maintain, and ensures good fractionating, contact between the metallic vapors and the conde iised'metalr The objects more."specifically.include the-provision of structural elements which permit 'the erection" of rfacdonating columns'of any: desired capacity, which are less managin and which, evenwhen sometail, do not necessitateiinmediat e interruption of cglun m operation as be noted that in the 'fractionating column shown in the grooves 15 byonly on'e' pair of opposite edge' portions,

whereas tray elements 17am" three edge portions fitted loosely'in horizontal grooves 15.' It is well to note that becausetwo'tray element's 16 are used rather than one large tray',iliquid5'l"alling,on these tray elements 16 will flow more; positively toibothibf the two 'weirs 19 disposed on opposite sides of these elements 16.

. r l 10 re esul in i smmes n -th .,Not only; do horizontal-grooves115. provide the sole supportfor, alliof-the trays in the Tfracti'onating column; but alsogthesegrooves promote tlieflow of"'liqu'idcondensed onwallsll, ,12,.13',:1'4, on'to tray'elements 16,117 Thatistosam hot vaporscondensed on'walls 11 12,13; liiwilllnot tendto flowdo'wn'the'full length :of thesewallsi but rather will tend to drip off. these walls promptly after being condensed along the upper side of horizontal grooves 15. The drops of condensed liquid fall on tray elements 16, 17 and join the liquid flowing as a shallow pool across the upper faces thereof to maintain good fractionating contact with the hot vapors. The edge portions along three sides of the rectangular shape of each tray element 16, 17 is thicker than the major portion of such tray element and a Weir 18 or 19 is provided along the fourth side of each tray element 17 or 16, respectively. The thicker edge portions of each tray element 16, 17 not only promote the flow of condensed liquid away from walls 11, 12, 13, 14 so as to bring this liquid in good fractionating contact with the hot vapors, but also the thicker edge portions provide maximum strength in tray elements 16, 17 at the support points.

The fractionating column of this invention is predicated on the use of refractory materialsrnecessitated by the high temperatures at which the column will be operated and/ or by the corrosive, erosive or like action of, the vapors. and liquid flowing through the column. Suitable refractory materials for exposure to zinc vapors and molten metal include graphite, high grade firebrick and silicon carbide. With the best refractory materials now available, it is advisable to make the maximum dirnension of tray elements not more than about 3 feet and the dimension at right angles thereto not more than about 2 feet.

In view of the fact that the joints, between blocks or bricks of the refractory materials used in they erection of the tower walls are prone to leak even at moderate pressures, it is highly, desirable'to minimize the pressure drop or differential along the vertical dimension ,of the frac tionating column. For this reason, it is advisable to dimension the tray at each level in the column so that it occupies from about 50% to about 80% of the opening bounded by the tower walls.

A specific example of the invention will now. be described with reference to a fractionating column for distilling zinc. Referring to Figures 1 and 2, each tray element 16 measures 2 feet 9 inches in length and 1 foot 6 inch in width; each tray element 17 has the same length but is 2 feet in width. Except for the edge portions, tray elements 16, 17 are 2 inches thick. Edge portions 0.8 inch wide are 3 inches thick along the two short sides and one long side of each tray element 16, 17, the other long side having a weir 19, 18 which is 0.8 inch wide and 2.5 inches high measured from the bottom face of the tray element. For a distance of 2 inches at each end of the weir side of each tray element 16, 17, the edge portion is also 0.8 inch wide and 3 inches thickso as to prevent the flow of molten zinc from the 0.5 inch deep pools on tlrgylilements 16, 17 against the interior surfaces of walls Horizontal grooves are 4 inches wide measured along the height of walls 11, 12, 13, 14. The vertical distance between the upper side of a groove 15 andthe lower sideof the next higher groove 15"is' 4 inches."

Grooves 15 are 1.5 inches deep which means that the uppersides of grooves 15 completely overhangor overlap the thick edge portions of tray'elements 16, 17 with a safety margin of about 0;7 inch. Accordingly, the flow of molten zinc condensed on walls 11,12, 13, 14 into'the pools on tray elements 16, 17 is ensured.

.The spacebetween each pair of tray elements 17 is l foot 9 inches wide so that elements 17 close off about grooves in the inner surface of the tower." Obviously,--

more than two tray elements may be used at eachlevel tray elements may follow several dilferent patterns designed to promote good contact between vapors and liquid. Accordingly, only such limitations should be imposed on the invention as are set forth in the appended claims.

' What is claimed is:

-"l. A fractionating column for metallic vapors formed of refractory materials, wherein hot metallic vapors are contacted with liquid metal condensed from said vapors, and flowing on vertically spaced trays in said column, which comprises a column'formed by vapor-tight solid refractory walls, vertically spaced horizontal grooves formed in the inner sides of said solid walls'of said column and a plurality of vertically spaced trays arranged with the edge portions of said trays fitted loosely and movablyin said grooves to provide the sole support'for said trays, each of said trays comprisinga plurality of similar tray elements disposed loosely and movably with respect toone another in saidgroovesproviding the sole support a for each said tray.

2. Thefractionating column of claim 1 wherein at least one pair of the tray elements at one level in said column abut one another while at: least one pair of the tray elements in each of the next lower and next higher levels in said column are laterally spaced from one another.

3. The fractionatingcolumn of claim 1 wherein edge portions of each tray are thicker than the major portion of that tray so that a pool of liquid may be retained on said major portion of that tray bysaid edge portions.

4. The fractionating column of claim 3 wherein the upper side of each horizontal groove completely overlaps grooves formed in the inner sides of at least one pair of said walls, a rectangular tray with one pair of opposite edge portions fitted loosely and movably in said grooves at each vertically spaced level in said tower to provide the solesupport for said tray, and a weir along one edge portion of each said tray at right angles to' said pair of edge portions fitted loosely and movably in said grooves, each said tray'comprising a plurality'of similar tray elements of rectangular shape disposed loosely and movably with respect to one another in said grooves providing the sole support for each said tray.

6. The fractionating column of claim 5 wherein each tray occupies from about 50% toabout of the opening in the tower.

7. The fractionating column of claimj wherein each tray element has edge portions along three sides of said rectangular shape" which arethickerthan the major portion ofeach said tray element.

8. The fractionating column of .claim 7 wherein the upperside of'e'ach horizontal groove completely overlaps the thicker edge 'portionsof the tray elements fitted loosely and movablyiin-that groove. p

References Cited in. the file at this patent UNITEDTSTATES' PATENTS 846,499 Murray 7 Mar. 12, 1907 862,314 Decker Aug. 6, 1907 1 891,110 Stevinsj June 16, 1908 1,994,349 I Gind er et Mar. 12, 1935 2,174,559 Andersonsetal. Oct. 3, 1939 2,557,605 Kohut' June 19, 1951 

